Considerable attention has been directed to providing improved corrosion protection to metallic surfaces. One method for providing this corrosion protection is by depositing one or various conversion coatings on the metal surfaces to form a coating which protects the metal against corrosion and also serves as a base for improving the adhesion of subsequently applied siccative organic finishes. Such conversion coatings are applied by treatment of the surfaces with solutions of various chemicals which react with the surface to form the desired coating. Among the commonly used conversion coating compositions are aqueous phosphate and chromate solutions.
Another method for providing improved corrosion protection to metallic surfaces involves electrodepositing a zinc or zinc alloy coating on the metal surface.
Solvent-based siccative organic coating compositions have been applied to metal surfaces such as by spraying, dipping, rolling, etc. Water-soluble and/or dispersible resin based paints and lacquers also may be utilized to coat metal surfaces, and these may be applied by electrophoresis. The electrophoretic application of paint and lacquer involves the phenomena of electro-osmosis and electrolysis, as well as electrophoresis. In this method, an electric current is passed through the paint or lacquer solution while the article to be painted is made an electrode in the paint or lacquer.
Although the above techniques have provided corrosion protection to metal surfaces, there continues to be a need for metals and metal surfaces exhibiting even higher corrosion protection and improved adhesion of siccative coatings to the metal.